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Miles AR, Hawrysh PJ, Hossein-Javaheri N, Buck LT. Taurine activates glycine and GABA A receptor currents in anoxia-tolerant painted turtle pyramidal neurons. ACTA ACUST UNITED AC 2018; 221:jeb.181529. [PMID: 30237241 DOI: 10.1242/jeb.181529] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 09/13/2018] [Indexed: 11/20/2022]
Abstract
Unlike anoxia-intolerant mammals, painted turtles can survive extended periods without oxygen. This is partly accomplished by an anoxia-mediated increase in gamma-aminobutyric acid (GABA) release, which activates GABA receptors and mediates spike arrest in turtle neurons via shunting inhibition. Extracellular taurine levels also increase during anoxia; why this occurs is unknown but it is speculated that glycine and/or GABAA/B receptors are involved. Given the general importance of inhibitory neurotransmission in the anoxia-tolerant painted turtle brain, we investigated the function of taurine as an inhibitory neuromodulator in turtle pyramidal neurons. Using whole-cell patch-clamp electrophysiological methods to record from neurons within a cortical brain sheet, we found that taurine depolarized membrane potential by ∼8 mV, increased whole-cell conductance ∼2-fold, and induced an inward current that possessed characteristics similar to GABA- and glycine-evoked currents. These effects were mitigated following glycine receptor antagonism with strychnine and GABAA receptor antagonism with gabazine, bicuculine or picrotoxin, but were unchanged following GABAB or glutamatergic receptor inhibition. These data indicate that a high concentration of taurine in vitro mediates its effects through both glycine and GABAA receptors, and suggests that taurine, in addition to GABA, inhibits neuronal activity during anoxia in the turtle cortex.
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Affiliation(s)
- Ashley R Miles
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
| | - Peter J Hawrysh
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5
| | | | - Leslie T Buck
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada M5S 3G5 .,Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, Canada, M5S 3G5
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The hypoxia-tolerant vertebrate brain: Arresting synaptic activity. Comp Biochem Physiol B Biochem Mol Biol 2018; 224:61-70. [DOI: 10.1016/j.cbpb.2017.11.015] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 11/23/2017] [Accepted: 11/30/2017] [Indexed: 01/16/2023]
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Christensen RK, Delgado-Lezama R, Russo RE, Lind BL, Alcocer EL, Rath MF, Fabbiani G, Schmitt N, Lauritzen M, Petersen AV, Carlsen EM, Perrier JF. Spinal dorsal horn astrocytes release GABA in response to synaptic activation. J Physiol 2018; 596:4983-4994. [PMID: 30079574 DOI: 10.1113/jp276562] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2018] [Accepted: 08/01/2018] [Indexed: 02/02/2023] Open
Abstract
KEY POINTS GABA is an essential molecule for sensory information processing. It is usually assumed to be released by neurons. Here we show that in the dorsal horn of the spinal cord, astrocytes respond to glutamate by releasing GABA. Our findings suggest a novel role for astrocytes in somatosensory information processing. ABSTRACT Astrocytes participate in neuronal signalling by releasing gliotransmitters in response to neurotransmitters. We investigated if astrocytes from the dorsal horn of the spinal cord of adult red-eared turtles (Trachemys scripta elegans) release GABA in response to glutamatergic receptor activation. For this, we developed a GABA sensor consisting of HEK cells expressing GABAA receptors. By positioning the sensor recorded in the whole-cell patch-clamp configuration within the dorsal horn of a spinal cord slice, we could detect GABA in the extracellular space. Puff application of glutamate induced GABA release events with time courses that exceeded the duration of inhibitory postsynaptic currents by one order of magnitude. Because the events were neither affected by extracellular addition of nickel, cadmium and tetrodotoxin nor by removal of Ca2+ , we concluded that they originated from non-neuronal cells. Immunohistochemical staining allowed the detection of GABA in a fraction of dorsal horn astrocytes. The selective stimulation of A∂ and C fibres in a dorsal root filament induced a Ca2+ increase in astrocytes loaded with Oregon Green BAPTA. Finally, chelating Ca2+ in a single astrocyte was sufficient to prevent the GABA release evoked by glutamate. Our results indicate that glutamate triggers the release of GABA from dorsal horn astrocytes with a time course compatible with the integration of sensory inputs.
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Affiliation(s)
- Rasmus Kordt Christensen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Rodolfo Delgado-Lezama
- Departamento de Fisiología, Biofísica y Neurociencias Cinvestav-IPN Avenida IPN 2508, Col. Zacatenco México City, CP, 07300, Mexico
| | - Raúl E Russo
- Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable, 11600, Montevideo, Uruguay
| | - Barbara Lykke Lind
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Emanuel Loeza Alcocer
- Departamento de Fisiología, Biofísica y Neurociencias Cinvestav-IPN Avenida IPN 2508, Col. Zacatenco México City, CP, 07300, Mexico
| | - Martin Fredensborg Rath
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Gabriela Fabbiani
- Neurofisiología Celular y Molecular, Instituto de Investigaciones Biológicas Clemente Estable, 11600, Montevideo, Uruguay
| | - Nicole Schmitt
- Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Martin Lauritzen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Anders Victor Petersen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Eva Meier Carlsen
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Jean-François Perrier
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
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Bartman ME, Johnson SM. Isolated adult turtle brainstems exhibit central hypoxic chemosensitivity. Comp Biochem Physiol A Mol Integr Physiol 2018; 225:65-73. [PMID: 30003967 DOI: 10.1016/j.cbpa.2018.07.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 06/27/2018] [Accepted: 07/03/2018] [Indexed: 10/28/2022]
Abstract
During hypoxia, red-eared slider turtles increase ventilation and decrease episodic breathing, but whether these responses are due to central mechanisms is not known. To test this question, isolated adult turtle brainstems were exposed to 240 min of hypoxic solution (bath PO2 = 32.6 ± 1.2 mmHg) and spontaneous respiratory-related motor bursts (respiratory event) were recorded on hypoglossal nerve roots. During hypoxia, burst frequency increased during the first 15 min, and then decreased during the remaining 35-240 min of hypoxia. Burst amplitude was maintained for 120 min, but then decreased during the last 120 min. The number of bursts/respiratory event decreased within 30 min and remained decreased. Pretreatment with either prazosin (α1-adrenergic antagonist) or MDL7222 (5-HT3 antagonist) blocked the hypoxia-induced short-term increase and the longer duration decrease in burst frequency. MDL7222, but not prazosin, blocked the hypoxia-induced decrease in bursts/respiratory event. Thus, during bath hypoxia, isolated turtle brainstems continued to produce respiratory motor output, but the frequency and pattern were altered in a manner that required endogenous α1-adrenergic and serotonin 5-HT3 receptor activation. This is the first example of isolated reptile brainstems exhibiting central hypoxic chemosensitivity similar to other vertebrate species.
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Affiliation(s)
- Michelle E Bartman
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Stephen M Johnson
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA.
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Abstract
Many environmental conditions can constrain the ability of animals to obtain sufficient food energy, or transform that food energy into useful chemical forms. To survive extended periods under such conditions animals must suppress metabolic rate to conserve energy, water, or oxygen. Amongst small endotherms, this metabolic suppression is accompanied by and, in some cases, facilitated by a decrease in core body temperature-hibernation or daily torpor-though significant metabolic suppression can be achieved even with only modest cooling. Within some ectotherms, winter metabolic suppression exceeds the passive effects of cooling. During dry seasons, estivating ectotherms can reduce metabolism without changes in body temperature, conserving energy reserves, and reducing gas exchange and its inevitable loss of water vapor. This overview explores the similarities and differences of metabolic suppression among these states within adult animals (excluding developmental diapause), and integrates levels of organization from the whole animal to the genome, where possible. Several similarities among these states are highlighted, including patterns and regulation of metabolic balance, fuel use, and mitochondrial metabolism. Differences among models are also apparent, particularly in whether the metabolic suppression is intrinsic to the tissue or depends on the whole-animal response. While in these hypometabolic states, tissues from many animals are tolerant of hypoxia/anoxia, ischemia/reperfusion, and disuse. These natural models may, therefore, serve as valuable and instructive models for biomedical research.
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Affiliation(s)
- James F Staples
- Department of Biology, University of Western Ontario, London, Ontario, Canada
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Fago A, Jensen FB. Hypoxia tolerance, nitric oxide, and nitrite: lessons from extreme animals. Physiology (Bethesda) 2015; 30:116-26. [PMID: 25729057 DOI: 10.1152/physiol.00051.2014] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Among vertebrates able to tolerate periods of oxygen deprivation, the painted and red-eared slider turtles (Chrysemys picta and Trachemys scripta) and the crucian carp (Carassius carassius) are the most extreme and can survive even months of total lack of oxygen during winter. The key to hypoxia survival resides in concerted physiological responses, including strong metabolic depression, protection against oxidative damage and-in air-breathing animals-redistribution of blood flow. Each of these responses is known to be tightly regulated by nitric oxide (NO) and during hypoxia by its metabolite nitrite. The aim of this review is to highlight recent work illustrating the widespread roles of NO and nitrite in the tolerance to extreme oxygen deprivation, in particular in the red-eared slider turtle and crucian carp, but also in diving marine mammals. The emerging picture underscores the importance of NO and nitrite signaling in the adaptive response to hypoxia in vertebrate animals.
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Affiliation(s)
- Angela Fago
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark; and
| | - Frank B Jensen
- Department of Biology, University of Southern Denmark, Odense, Denmark
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Keenan SW, Hill CA, Kandoth C, Buck LT, Warren DE. Transcriptomic Responses of the Heart and Brain to Anoxia in the Western Painted Turtle. PLoS One 2015; 10:e0131669. [PMID: 26147940 PMCID: PMC4493013 DOI: 10.1371/journal.pone.0131669] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2015] [Accepted: 06/05/2015] [Indexed: 12/23/2022] Open
Abstract
Painted turtles are the most anoxia-tolerant tetrapods known, capable of surviving without oxygen for more than four months at 3°C and 30 hours at 20°C. To investigate the transcriptomic basis of this ability, we used RNA-seq to quantify mRNA expression in the painted turtle ventricle and telencephalon after 24 hours of anoxia at 19°C. Reads were obtained from 22,174 different genes, 13,236 of which were compared statistically between treatments for each tissue. Total tissue RNA contents decreased by 16% in telencephalon and 53% in ventricle. The telencephalon and ventricle showed ≥ 2x expression (increased expression) in 19 and 23 genes, respectively, while only four genes in ventricle showed ≤ 0.5x changes (decreased expression). When treatment effects were compared between anoxic and normoxic conditions in the two tissue types, 31 genes were increased (≥ 2x change) and 2 were decreased (≤ 0.5x change). Most of the effected genes were immediate early genes and transcription factors that regulate cellular growth and development; changes that would seem to promote transcriptional, translational, and metabolic arrest. No genes related to ion channels, synaptic transmission, cardiac contractility or excitation-contraction coupling changed. The generalized expression pattern in telencephalon and across tissues, but not in ventricle, correlated with the predicted metabolic cost of transcription, with the shortest genes and those with the fewest exons showing the largest increases in expression.
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Affiliation(s)
- Sarah W. Keenan
- Department of Biology, Saint Louis University, St. Louis, Missouri, United States of America
| | - Craig A. Hill
- Department of Biology, Saint Louis University, St. Louis, Missouri, United States of America
| | - Cyriac Kandoth
- The Genome Institute, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Leslie T. Buck
- Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Daniel E. Warren
- Department of Biology, Saint Louis University, St. Louis, Missouri, United States of America
- * E-mail:
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8
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Turtle anoxia tolerance: Biochemistry and gene regulation. Biochim Biophys Acta Gen Subj 2015; 1850:1188-96. [DOI: 10.1016/j.bbagen.2015.02.001] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2014] [Accepted: 02/01/2015] [Indexed: 12/16/2022]
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Jonz MG, Buck LT, Perry SF, Schwerte T, Zaccone G. Sensing and surviving hypoxia in vertebrates. Ann N Y Acad Sci 2015; 1365:43-58. [PMID: 25959851 DOI: 10.1111/nyas.12780] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2015] [Revised: 03/26/2015] [Accepted: 03/31/2015] [Indexed: 12/15/2022]
Abstract
Surviving hypoxia is one of the most critical challenges faced by vertebrates. Most species have adapted to changing levels of oxygen in their environment with specialized organs that sense hypoxia, while only few have been uniquely adapted to survive prolonged periods of anoxia. The goal of this review is to present the most recent research on oxygen sensing, adaptation to hypoxia, and mechanisms of anoxia tolerance in nonmammalian vertebrates. We discuss the respiratory structures in fish, including the skin, gills, and air-breathing organs, and recent evidence for chemosensory neuroepithelial cells (NECs) in these tissues that initiate reflex responses to hypoxia. The use of the zebrafish as a genetic and developmental model has allowed observation of the ontogenesis of respiratory and chemosensory systems, demonstration of a putative intracellular O2 sensor in chemoreceptors that may initiate transduction of the hypoxia signal, and investigation into the effects of extreme hypoxia on cardiorespiratory development. Other organisms, such as goldfish and freshwater turtles, display a high degree of anoxia tolerance, and these models are revealing important adaptations at the cellular level, such as the regulation of glutamatergic and GABAergic neurotransmission in defense of homeostasis in central neurons.
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Affiliation(s)
- Michael G Jonz
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Leslie T Buck
- Cell and Systems Biology, and Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
| | - Steve F Perry
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | | | - Giacomo Zaccone
- Department of Environmental Sciences, Territorial, Food and Health Security (S.A.S.T.A.S.), University of Messina, Messina, Italy
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Smith RW, Cash P, Hogg DW, Buck LT. Proteomic changes in the brain of the western painted turtle (Chrysemys picta bellii) during exposure to anoxia. Proteomics 2015; 15:1587-97. [PMID: 25583675 DOI: 10.1002/pmic.201300229] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 10/03/2014] [Accepted: 01/09/2015] [Indexed: 01/10/2023]
Abstract
During anoxia, overall protein synthesis is almost undetectable in the brain of the western painted turtle. The aim of this investigation was to address the question of whether there are alterations to specific proteins by comparing the normoxic and anoxic brain proteomes. Reductions in creatine kinase, hexokinase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase reflected the reduced production of adenosine triphosphate (ATP) during anoxia while the reduction in transitional endoplasmic reticulum ATPase reflected the conservation of ATP or possibly a decrease in intracellular Ca(2+). In terms of neural protection programed cell death 6 interacting protein (PDCD6IP; a protein associated with apoptosis), dihydropyrimidinase-like protein, t-complex protein, and guanine nucleotide protein G(o) subunit alpha (Go alpha; proteins associated with neural degradation and impaired cognitive function) also declined. A decline in actin, gelsolin, and PDCD6IP, together with an increase in tubulin, also provided evidence for the induction of a neurological repair response. Although these proteomic alterations show some similarities with the crucian carp (another anoxia-tolerant species), there are species-specific responses, which supports the theory of no single strategy for anoxia tolerance. These findings also suggest the anoxic turtle brain could be an etiological model for investigating mammalian hypoxic damage and clinical neurological disorders.
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Affiliation(s)
- Richard W Smith
- Department of Medical Physics and Applied Radiation Sciences, McMaster University, Hamilton, ON, Canada
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Galli GLJ, Richards JG. Mitochondria from anoxia-tolerant animals reveal common strategies to survive without oxygen. J Comp Physiol B 2014; 184:285-302. [DOI: 10.1007/s00360-014-0806-3] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2013] [Revised: 01/09/2014] [Accepted: 01/17/2014] [Indexed: 12/15/2022]
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Madsen JG, Wang T, Beedholm K, Madsen PT. Detecting spring after a long winter: coma or slow vigilance in cold, hypoxic turtles? Biol Lett 2013; 9:20130602. [PMID: 24108677 DOI: 10.1098/rsbl.2013.0602] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Many freshwater turtle species can spend the winter submerged in ice-covered lakes by lowering their metabolism, and it has been proposed that such severe metabolic depression render these turtles comatose. This raises the question of how they can detect the arrival of spring and respond in a sensible way to sensory information during hibernation. Using evoked potentials from cold or hypoxic turtles exposed to vibration and light, we show that hibernating turtles maintain neural responsiveness to light stimuli during prolonged hypoxia. Furthermore, turtles held under hibernation conditions for 14 days increase their activity when exposed to light or elevated temperatures, but not to vibration or increased oxygen. It is concluded that hibernating turtles are not comatose, but remain vigilant during overwintering in cold hypoxia, allowing them to respond to the coming of spring and to adjust their behaviour to specific sensory inputs.
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Affiliation(s)
- Jesper G Madsen
- Zoophysiology, Department of Bioscience, Aarhus University, , Building 1131, 8000 Aarhus, Denmark
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